The present disclosure generally relates to appliances, and more particularly, to detecting airflow, and/or measuring airflow velocity, in a cooling pathway of an appliance.
Appliances such as cooking ranges are widely used. A cooking range typically includes an oven. The oven typically has a front-opening access door, and at least one heating element for heating up the inside of the oven cavity. As is known in the art, when energized, the heating element can heat up the inside of the oven cavity to a relatively high cooking temperature chosen by a user. Also as is known in the art, the cooking range often has a fan which is used to cool a component of the oven, such as the front-opening access door, or a heat sensitive component of the oven such as an electrical element (e.g., electronic controller, display unit, etc.), to a temperature which is lower than the chosen cooking temperature. Some certification institutions, such as Underwriters Laboratories Inc. (UL), require that a Fan Apparency Device (FAD) be employed in the cooking range. The FAD is used to determine or detect whether the fan is working properly, that is, whether or not airflow is being created by the cooling fan.
As is known in the art, when a user selects or chooses a heating operation of the oven and turns on the oven, the turning-on supposedly activates the fan. The FAD then determines or detects whether the fan is working properly. If the fan is working properly, the FAD enables the selected heating operation of the oven to proceed. On the other hand, if the fan is not working properly, the FAD prevents the selected heating operation of the oven from proceeding. Various types of FADs are used to determine or detect whether the fan is working properly.
The most widely used FADs are thermal switches and sail switches. A thermal switch uses the heat from the oven to heat up a bimetal member of the switch to turn off the switch when the airflow from the fan is no longer present to cool off the bimetal member. Since the thermal switch usually is not disposed adjacent the intake end or the discharge end of the fan, it does not negatively affect the airflow passing through the fan. However, the thermal switch has a relatively slow reaction time. In addition, the thermal switch needs to be installed in an area of the oven where the temperature can raise quickly when the oven is turned on. Moreover, the thermal switch requires a significant amount of calibration and testing to prove that it will work as intended in all working conditions of the oven.
A typical sail switch uses the airflow generated by the fan to move a sail, typically a large, flat piece of sheet metal, to turn on or off the switch, Sail switches often include a spring return for returning the sail. Compared with the thermal switch, the sail switch has a very fast reaction time, and requires significantly less time/effort to implement. However, the sail switch has its own limitations. In particular, when it is desirable to direct or point the exhaust end or discharge end of the fan toward the floor on which the appliance is placed, it can be difficult to satisfactorily employ the sail switch in this configuration. This is because in this configuration, the positive pressure side of the sail, which is positioned downstream of the fan, has to face up. As a result, the weight of the sail constantly urges the sail to move from its upper position where the sail opens the switch to its lower position where the sail closes the switch. To make matters worse, in this configuration the positive pressure side of the sail tends to collect a noticeable amount of dust particulates, grease, etc. All of these contribute to the problem that the sail may move to and stay in its lower position even when the fan is not activated, thus creating a false indication of the working condition of the fan. Sail switches also tend to be constructed of thin, flimsy metal and are easily damaged or knocked out of calibration during repair operations and abusive shipping disturbances (drops). Sail switches have also been prone to producing rattling/chattering noises, thus disturbing/annoying the operator of the appliance (also known as the consumer).